1. Field of the Invention
The present invention relates to in-wheel motors, and particularly to in-wheel motors capable of efficiently cooling their motors.
2. Description of the Background Art
Conventional in-wheel motors include a motor, an oil pump, a case and a wheel disc. The case is comprised of a motor chamber and a pump chamber. The motor is housed in the motor chamber of the case and the oil pump is housed in the pump chamber of the case.
The case containing the motor and the oil pump is placed to face the wheel disc. The oil pump circulates an oil stored in an oil reservoir to cool stator coils of the motor (Japanese Patent Laying-Open No. 5-338446).
In this way, the conventional in-wheel motor cools the motor with the circulating oil.
The cooling method disclosed in Japanese Patent Laying-Open No. 5-338446, however, encounters a problem of insufficient cooling of the motor since it is only the oil pump that circulates the oil.
In order to satisfactorily circulate the oil, the oil circulation structure has to be increased in size, which is an additional problem of the conventional cooling method.
Moreover, the cooling method disclosed in Japanese Patent Laying-Open No. 5-338446 encounters a further problem of insufficient cooling of one of the longitudinal ends of each of stator coils that is located relatively further from the oil pump.